=====================
Kid 0.6 Release Notes
=====================

There has been significant change in version 0.6. This includes enhancements
and modifications to the template language and python interface.

.. contents:: Contents

Language and API Changes
========================

The following changes are likely to impact existing code and
templates. Where possible, we have tried to maintain backward compatibility
but that wasn't possible in all cases.

The `Upgrade Script`_ can be used to bring 0.5 templates up to 0.6 syntax.


Kid Namespace Change
--------------------

The Kid namespace has changed from ``http://naeblis.cx/ns/kid#`` to
``http://purl.org/kid/ns#``. The naeblis.cx domain is privately owned and
could expire some time in the future. purl.org is a system for establishing
and maintaining "persistent" URIs.

A temporary hack has been put in place to substitute references to the old
namespace URI with the new namespace URI. A warning is output when this
occurs. This will be removed in a couple of months so it is recommended that
templates be upgraded as soon as possible.


``py:omit`` is now ``py:strip``
-------------------------------

Due to initial confusion many experienced with the name ``py:omit``, it has
been renamed ``py:strip``. The term "omit" was often read as "omit the
element and all descendants". The new term "strip" seems to better indicate
the semantic: "strip the start and end tag but process descendants."

Python Expression Substitution Syntax
-------------------------------------

The syntax of brace expansions has been modified match more closely with
existing Python substitution syntax. In 0.5 python expressions enclosed in
curly braces ({}) were evaluated and their results substituted. In 0.6, the
rules have changed as follows:

  1. ``$$`` is an escape; it is replaced with a single $.
  2. ``$name`` substitutes a variable value.
  3. ``${expr}`` substitutes the result of evaluating any python expression.

See `Python Expression Substitution`__ in the Language Reference.

.. __: language.html#python-expression-substitution-expr

.. warning:

  The expression substitution **is not** backward compatible. If you use the
  old-style brace-expansion, you will need to upgrade your templates for Kid
  0.6.

Enhancements
============

cElementTree Support
--------------------

Kid now uses cElementTree if it is available. Preliminary tests show
moderate performance increases. In most cases, we're seeing template parse
and execution time increase by about 15%. The poor increase (relative to
other cET/ET numbers) is due to the fact that we're not using cElementTree's
native parser as it doesn't support comments or processing instructions. The
plan is to lobby the effbot organization to add these features (hint, hint:
send patches) so that we can get the huge increases people are seeing
elsewhere.

Kid automatically determines whether cElementTree is available and uses it
if so. If cElementTree is not available, Kid falls back on Python
ElementTree. If you want to turn off use of cElementTree, you can set the
environment variable ``KID_NOCET`` to 1.

Death of Comment Wart
---------------------

In versions of Kid prior to 0.6, the first line of an embedded Python code
block had to be a Python comment (#). This was due to Python's whitespace
semantics. Christoph determined a process for establishing the correct indent
levels without requiring a comment as the first line.

Starting in Kid 0.6, a comment is no longer required to be the first line in
a ``<?python?>`` processing instruction. It is also possible to have single
line code blocks::

 <?python x = 10 ?>


Improved Template API
---------------------

The Python interfaces have been reworked significantly and now are very
similar to Cheetah's. There are two preferred methods for accessing a
template.

The ``Template`` Class
~~~~~~~~~~~~~~~~~~~~~~

The first method existed in 0.5 but was not documented well. If you have
enabled the kid import hooks, then you can import a template and create an
instance of the template by accessing the ``Template`` class exposed by the
module::

  import kid ; kid.enable_import()
  import mytemplate
  template = mytemplate.Template(foo='bar', bling=1)
  print template.serialize()

The primary difference from 0.5 is that template variables are passed to the
``Template`` constructor instead of to the individual execution methods
(``serialize``, ``generate``, ``write``, ``pull``).

It is also possible to set template variables after the template instance
is created by simply assigning to template object instance::

  template = mytemplate.Template()
  template.foo = 'bar'
  template.bling = 1
  print str(template)

Here we see another small addition: template instances implement ``__str__``
and ``__unicode__`` built-ins. These methods are equivalent to calling
``serialize(encoding='utf-8')`` and ``serialize(encoding='utf-16')``,
respectively.

The ``kid.Template`` function
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The ``kid.Template`` function works much like ``Template`` class
constructors but takes an additional parameter that allows the template to
be loaded from a file, string, or module name. It is sometimes easier to
manage templates as files on disk rather than as python modules.

Example::

  from kid import Template
  # create a template from file
  template = Template(file='mytemplate.kid', foo='bar', bling=1)

  # create a template from string
  template = Template(source="<p>${foo}</p>", foo='bar')

  # create a template from a python module name
  template = Template(name='templates.mytemplate', foo='bar')

This last form is sometimes useful because it doesn't require the kid
import hook to be enabled and it also allows template names to be specified
at run-time.

See `kid.Template function`__ in the User's Guide for more info.

.. __: guide.html#template-function


Match Templates / Filters
-------------------------

Match Templates are a cross between XSLT's match templates and JSP tag
libraries. They allow a set of filters to be put in place that matches
infoset items generated by a template so that output can be modified.

While match templates provide a general purpose mechanism for transforming
XML content, it is especially useful in a couple of situations which have
driven the design:

1. Creating tag libraries that inject new tags into an XML vocabulary.

2. Applying headers/footers without inserting place-holders into the
   source document/template.

See `Match Templates`__ in the Language Reference for more information.

.. __: language.html#match-templates

Template Inheritance
--------------------

Templates now support multiple inheritance of template functions
(``py:def``) and match templates (``py:match``). A template indicates that
it extends one or more other templates by setting the ``py:extends``
attribute on the root element::

  <?xml version='1.0' encoding='utf-8'?>
  <html py:extends="'common.kid', 'forms.kid'" ...

``py:extends`` may contain template modules, Template classes, or strings
specifying template paths relative to current template file.

See `Template Reuse`__ in the Language Reference for more information.

.. __: language.html#template-reuse


Dynamic Attribute Generation (``py:attrs``)
-------------------------------------------

A new ``py:attrs`` attribute has been added that allows attributes to be
specified using a dictionary.

See `Dynamic Attributes`__ in the Language Reference for more information.

.. __: language.html#dynamic-attributes-py-attrs


Upgrade Script
==============

Due to the amount of changes in template syntax, a migration script is
provided that can upgrade kid 0.5 templates to 0.6 syntax. This includes
changing the namespace, py:strip, and new expression substitution
syntax.

The script can be found in the source distribution as
``misc/upgrade-0.6.py``. The script can take multiple file names and
upgrades each in-place while preserving a backup. For instance::

  $ python upgrade-0.6.py path/to/template.kid
  Upgraded: template.kid...

On posix systems, you can upgrade a bunch of kid templates under the current
working directory with the following command::

  $ find . -name '*.kid' | xargs python upgrade-0.6.py
  Upgraded: template1.kid...
  Upgraded: template2.kid...
  Upgraded: template3.kid...
  Upgraded: template4.kid...
